Overview

In this chapter, we discuss some of the other well-documented K–T boundary localities in North America outside of the Williston Basin. These localities are situated in other sedimentary basins in a south-to-north corridor from New Mexico to Alaska, including parts of western Canada (Figure 7.1). Collectively these localities contribute to a large database of information about plants and the K–T boundary, although it will became clear to the reader that the quality of the records varies from one to the next. The south-to-north geographic distribution of these basins constitutes a proximal-to-distal array with respect to the postulated K–T impact crater on the Yucatan Peninsula of Mexico. This fact appears to have particular relevance with respect to preservation of a boundary claystone layer and other indicators of the K–T boundary discussed in Section 2.3, such as shocked minerals.

Raton Basin, Colorado and New Mexico

The first iridium-bearing terrestrial K–T boundary sections were discovered in the Raton Basin of southeastern Colorado and northeastern New Mexico (Figure 7.2). The K–T boundary is preserved in the Raton Formation, an entirely nonmarine unit of Maastrichtian and early Paleocene age (Figure 7.3). The Raton Formation is composed of sandstone, siltstone, mudstone, coal, and minor conglomerate. Thin to thick coal beds are common in the lower and upper parts of the formation, but are scarce to absent in the middle “barren series,” which is composed largely of sandstone.

Overview

The quality of published K–T boundary terrestrial data diminishes dramatically outside of North America. Of the 20 non-North American K–T boundary sections, only one scored as much as 10 points on Table 2.1. Our evaluation of these sections begins with the 14 localities known from Eurasia, which we subdivide based on the data available into Europe, Japan, China, and the Russian Far East. Each of these regions is discussed in its own section in this chapter.

Two of the first three places in the world where an iridium anomaly was found at the K–T boundary are in Europe. However, detailed paleobotanical and palynological records of the event are absent at those localities because the boundary occurs in marine rocks. The microfossils that record extinction at the K–T boundary in those places are marine foraminifera, and although they provide an excellent fossil record of the event, they reveal nothing about land plants and the boundary. There are some nonmarine rocks spanning the boundary in Europe, however, and we review the published records from those areas. Abundant nonmarine rock sequences are to be found in Asia, especially in northeast China and the Russian Far East, and extensive literature is available. We have supplemented the Asian literature with our own field work.

A comparison of palynomorph assemblages from Upper Cretaceous and lower Paleogene intervals in western Europe, northwest Africa, and southeast China by Song and Huang (1997) provides an overview of the distribution of plants in those areas at that time, based on palynological records published through 1996 (see also Chapter 5).

The K–T controversy and the Alvarez challenge

A paper published in 1980 in the journal Science revolutionized the science of geology. Coauthored by Nobel laureate in physics Luis Alvarez, his geophysicist son Walter, and two colleagues, the paper presented data from the esoteric field of neutron activation analysis. These data suggested that the Earth had been struck by a large extraterrestrial object (an asteroid or possibly a comet) some 65 million years ago, precisely at the moment in time that marked the boundary between the Mesozoic and Cenozoic eras (Figure 1.1). The time line, on a smaller scale also the boundary between the Cretaceous and Paleogene periods, was widely known as the K–T boundary (“K” being the internationally accepted abbreviation for Cretaceous and “T” being the corresponding abbreviation for either Tertiary or Paleogene, according to nomenclatural preference). The paper (Alvarez et al. 1980) also proposed that this extraterrestrial impact had been responsible for one of the greatest episodes of extinction in Earth history. The K–T extinctions, which eradicated 70% or more of species on land and in the sea, ended the Mesozoic Era, the second of the three great subdivisions of life recognized by paleontologists. The cause of the K–T extinctions had long been argued in paleontology. The impact hypothesis had now been put forward as the explanation.

The asteroid impact hypothesis, involving as it does a causative agent from outside the Earth and also an instantaneous catastrophic event (an anathema in geology in 1980), immediately became enormously controversial in paleontology and geology.

The study of palynoflora

Palynofloras are essential to studies of the K–T boundary in nonmarine rocks. Numerous aspects of the nature of palynofloras must be considered when using them in such studies. These include: taxonomy (pollen or spore species vs. botanical species), preservation and preparation, sample size, facies effects, reworking or redeposition, stratigraphic resolution, and geographic coverage. These topics are covered in depth in textbooks on palynology (e.g., Traverse 1988b, Jansonius and McGregor 1996, Jones and Rowe 1999), but to be complete in our coverage of the use of palynofloras to study the K–T boundary, each of these topics is briefly discussed in this section.

Most genera of angiosperms (flowering plants) produce pollen with distinguishing morphologic features unique to those genera (number of apertures, exine structure and sculpture, size, etc.), which are the basis of palynological taxonomy. Most species within individual genera share the same characteristic features. Hence, whereas individual living and fossil genera can be differentiated, in most cases individual species cannot. Therefore, as a general rule, fossil pollen species can be thought of as representing botanical genera in the fossil record, and fossil pollen genera can be thought of as representing botanical families. This generality complicates the comparison between palynofloral and megafloral systematics. Comprehensive descriptions of the pollen morphology of living genera and species are in Edrtman (1965, 1966), and discussions and examples of the relationships of fossil pollen taxa to botanical taxa are in Muller (1970) and Traverse (1988b).

XANTHOPHYCEAE

The Xanthophyceae contain primarily freshwater and terrestrial algae with a few marine representatives. The class is characterized by motile cells with a forwardly directed tinsel flagellum and a posteriorly directed whiplash flagellum (Figs. 19.1, 19.5(c)). The chloroplasts contain chlorophylls a and c (Sullivan et al., 1990), lack fucoxanthin, and are colored yellowish-green. The eyespot in motile cells is always in the chloroplast (Figs. 19.1, 19.5(c)), and the chloroplasts are surrounded by two membranes of chloroplast endoplasmic reticulum. The outer membrane of the chloroplast E.R. is usually continuous with the outer membrane of the nucleus. In most non-motile cells the wall is composed of two overlapping halves (Figs. 19.2 (d), (e), (f), 19.3, 19.4). Molecular data have shown the Xanthophyceae is most closely related to the Phaeophyceae (Ariztia et al., 1991; Potter et al., 1997). Although the class is commonly called the Xanthophyceae, the proper name is the Tribophyceae since there is no genus in the class that can lend its name to Xanthophyceae (Hibberd, 1981).

Cell structure

Cell wall

Cell wall The cell walls of two Xanthophyceae, Tribonema (Figs. 19.2, 19.3) (Cleare and Percival, 1973) and Vaucheria (Figs. 19.7, 19.8), are composed of cellulose (Parker et al., 1963). In Vaucheria cellulose comprises 90% of the wall, with the remaining portion being amorphous polysaccharides composed primarily of glucose and uronic acids.

Many of the algae in the class have walls composed of two overlapping halves that fit together as do the two parts of the bacteriologist's Petri dish (Figs. 19.2(d), (e), (f), 19.3, 19.4).

SYNUROPHYCEAE

The Synurophyceae are closely related to the Chrysophyceae (Ariztia et al., 1991). The Synurophyceae differ, however, from the Chrysophyceae in the following: the Synurophyceae have chlorophylls a and c1 (Andersen and Mulkey, 1983), the flagella are inserted into the cell approximately parallel to one another (Fig. 11.1), there is a photoreceptor near the base of each flagellum, there is no eyespot, and the contractile vacuole is in the posterior portion of the cell (Lavau et al., 1997; Andersen et al., 1999). Chloroplast endoplasmic reticulum is present in a few species, but absent inmost. The cells usually are covered by bilaterally symmetrical scales.

In the Synurophyceae, scales composed of silica commonly occur outside the cell (Figs. 11.1, 11.2). The scales are bilaterally symmetrical and are formed in a silica deposition vesicle. The membrane of the silica deposition vesicle (the silicalemma) controls the shape of the scale along with proteins and glycoproteins that adhere the developing scale to the silicalemma (Schultz et al., 2001). The presence of germanium in the medium results in inhibition of scale formation (Klaveness and Guillard, 1975). The scales are carried in the scale vesicle to the plasma membrane where the plasma membrane and the scale vesicle fuse, releasing the scales outside the cell (Beech et al., 1990). The scales are held next to the cell in an organic envelope (Ludwig et al., 1996), which is either hyaline or yellow-brown, the latter appearance being due to the impregnation of iron salts.

BOLIDOPHYCEAE

This is a small order of flagellated marine picophytoplankton that is related to the diatoms (Bacillariophyceae) (Guillou et al., 1999). The cells contain chlorophylls a, c1, c2, c3, β-carotene, diatoxanthin, and fucoxanthin, as do the diatoms, It is probable that the diatoms originated from a motile ancestor similar to those in this class (although there is no report of silicification in the Bolidophyceae).

Bolidomonas is a unicell with a long tinsel flagella bearing tripartite tubular hairs and a shorter smooth flagellum (Fig. 16.1). The cell is only 1.2 μm in diameter and has a simple internal organization. There is one plastid, mitochondrion, and Golgi apparatus. There are two membranes of chloroplast endoplasmic reticulum, with the outer membrane continuous with the outer membrane of the nuclear envelope. The DNA is contained within a ring-shaped genophore and there is no eyespot.

The algae in the Heterokontophyta usually have cells with an anterior tinsel and posterior whiplash flagellum (Fig. 10.1). The plastids contain chlorophylls a and c along with fucoxanthin. The storage product is usually chrysolaminarin in cytoplasmic vesicles.

The following classes are commonly recognized (Andersen, 2004):

1. Chrysophyceae (golden-brown algae) (Chapter 10)

2. Synurophyceae (Chapter 11)

3. Eustigmatophyceae (Chapter 12)

4. Pinguiophyceae (Chapter 13)

5. Dictyochophyceae (silicoflagellates) (Chapter 14)

6. Pelagophyceae (Chapter 15)

7. Bolidophyceae (Chapter 16)

8. Bacillariophyceae (diatoms) (Chapter 17)

9. Raphidophyceae (chloromonads) (Chapter 18)

10. Xanthophyceae (yellow-green algae) (Chapter 19)

11. Phaeothamniophyceae (Chapter 20)

12. Phaeophyceae (brown algae) (Chapter 21)

CHRYSOPHYCEAE

The Chrysophyceae are distinguished chemically by having chlorophylls a, c1, and c2 (Andersen and Mulkey, 1983) and structurally by two flagella inserted into the cell perpendicular to each other, one photoreceptor on the short flagellum that is usually shaded by an eyespot in the anterior portion of the chloroplast, contractile vacuoles in the anterior portion of the cell, chloroplast endoplasmic reticulum, and radially or biradially symmetrical silica scales (if they are present). The storage product is chrysolaminarin. Many members of the class produce statospores enclosed in a silicified wall with a terminal pore.

Most of the species in the Chrysophyceae are freshwater and occur in soft waters (low in calcium). Many of the freshwater species are in the plankton of lakes where they are present in abundance. The coccoid and filamentous genera are found mostly in cold springs and brooks, where they occur as gelatinous or crustous growths on stones and woodwork. Most of the Chrysophyceae are sensitive to changes in the environment and survive the unfavorable periods as statospores.

It is possible to write whole books on the relationships between algae and the environment. In this chapter I have chosen a few subjects which have generated the most interest in the last decade.

Toxic algae

Algae can be harmful in two basic ways (Hallegraeff et al., 2003).

1. Producing large populations in the aquatic environment Large growths of some algae (e.g., the diatom Chaetoceros (Figs. 17.44, 17.45) or the prymnesiophyte Chrysochromulina (Fig. 23.1(c))) can clog the gills of fish and can be particularly a problem in aquaculture systems. Anoxic conditions, resulting in fish kills, can occur at the end of blooms of other algae (e.g., green algae) as the algae die and decompose.

2. Production of toxins Some algae produce toxins that sicken and kill other organisms that prey on these algae. Indeed, this probably was the reason that these algae were selected for in the evolutionary process since it reduced predation by grazers (Gilbert, 1996). Filter-feeding shellfish can accumulate large quantities of these toxins as they filter the algae out of the water. Consumption of the shellfish by man, birds, and animals results in sickness and death.

The algae that produce phycotoxins are:

Cyanophyceae (cyanobacteria)

• Neurotoxinsanatoxin (Fig. 23.2(c)) and saxitoxin (Fig. 23.2(c)) that block the transmission of signal from neuron to neuron. These alkaloids (nitrogen containing compounds) bind to voltage-activated Na+ -channels and block influx of Na+, thereby preventing the generation of an action potential (Shimizu, 2000).

• […]

The Rhodophyta (red algae) and Chlorophyta (green algae) form a natural group of algae in that they have chloroplasts surrounded by only the two membranes of the chloroplast envelope. The evolutionary event that led to the chloroplast occurred as follows (Fig. III.1). A phagocytotic protozoan took up a cyanobacterium into a food vesicle. Instead of being digested as a source of food, the cyanobacterium lived as an endosymbiont in the protozoan. This event benefited the protozoan because it received some of the photosynthate from the endosymbiotic alga, and it benefited the cyanobacterium because it received a protected stable environment. Through evolution the wall of the endosymbiotic cyanobacterium was lost. A mutation in the endosymbiont which resulted in a loss of the wall would have been selected for in evolution because it would have facilitated the transfer of compounds between the host and the endosymbiont. The food vesicle membrane of the phagocytotic host became the outer membrane of the chloroplast envelope. The plasma membrane of the cyanobacterium symbiont became the inner membrane of the chloroplast envelope. Rearrangement of the thylakoid membranes and evolution of polyhedral bodies into a pyrenoid completed the transition to a true chloroplast such as occurs in extant green and red algae.

The endosymbiotic origin of chloroplasts was first proposed by the Russian biologist Konstantin Mereschkowsky (1855–1921) (Fig. III.2) with the fundamentals of the idea appearing in his 1905 work, The Nature and Origins of Chromatophores in the Plant Kingdom (see Martin and Kowallik, 1999, for English translation).

PHAEOPHYCEAE

The Phaeophyceae, or brown algae, derive their characteristic color from the large amounts of the carotenoid fucoxanthin in their chloroplasts as well as from any phaeophycean tannins that might be present. The chloroplasts also have chlorophylls a, c1, and c2. There are two membranes of chloroplast E.R., which are usually continuous with the outer membrane of the nuclear envelope. The storage product is laminarin. There are no unicellular or colonial organisms in the order, and the algae are basically filamentous, pseudoparenchymatous, or parenchymatous. They are found almost exclusively in the marine habitat, there being only four genera containing freshwater species, that is, Heribaudiella, Pleurocladia, Bodanella, and Sphacelaria (Fig. 21.1) (Schloesser and Blum, 1980). A number of marine forms penetrate into brackish water, where they often form an important part of the salt marsh flora. These brackish water plants have almost totally lost the ability to reproduce sexually, and propagate by vegetative means only. Most of the Phaeophyceae grow in the intertidal belt and the upper littoral region. They dominate these regions in colder waters, particularly in the Northern Hemisphere, where the number of phaeophycean species is less than that of the Rhodophyceae, but the number of phaeophycean plants is much greater. In the tropics, the only place where large numbers of Phaeophyceae are found is the Sargasso Sea of the Atlantic.

The Phaeophyceae probably evolved from an organism in the Phaeothamniophyceae, which have motile cells similar to those in the Phaeophyceae, but lack the characteristic unilocular and plurilocular sporangia of the Phaeophyceae (Bailey et al., 1998).

It was that eccentric British soldier of fortune Col. Meinertzhagen, in his Birds of Arabia, who expressed the sentiment that prefaces should be kept short because few people ever read them. Accordingly, I would like to take a brief opportunity to express my gratitude to the people who offered encouragement and assistance during the preparation of this book. I would like to thank Adele Strauss Wolbarst, Robert Cnoops, Charmaine Slack, Sophia Skiordis, Caroline Mondel, Jill Keetley-Smith, Heather Edwards, Gail Arbeter, and the Lending Library at Boston Spa, England, for help while most of this manuscript was being prepared at the University of the Witwatersrand. For general encouragement while at Pahlavi (Shiraz) University and for providing assistance during the last turbulent and chaotic year of imperial rule in Iran, while the manuscript was being finished, I would like to thank Mark Gettner, Brian Coad, and Mumtaz Bokhari.

When photographs or drawings have been taken directly from the original material, this is indicated by stating in the legend that it is from the original work. Most of the drawings have been redrawn to suit my tastes, and these drawings are indicated by stating that the work is after the original. In some cases I have made drawings from photographs or have incorporated a number of drawings in one, in which case I state that the finished drawing is adapted from the original work or works.

The Euglenophyta (euglenoids), Apicomplexa, and Dinophyta (dinoflagellates) are a natural grouping in that they are the only algal groups to have one membrane of chloroplast endoplasmic reticulum. Chloroplast endoplasmic reticulum evolved when a chloroplast from a eukaryotic alga was taken into a food vesicle by a phagocytotic euglenoid, apicomplexan or dinoflagellate (Fig. IV.1) (Lee, 1977; Gibbs, 1978). Normally the cell would have digested the chloroplast as a source of food. However, in this case the chloroplast remained in the cytoplasm of the host as an endosymbiont. The host benefited from the association by receiving photosynthate from the endosymbiotic chloroplast. The endosymbiotic chloroplast benefited from the high concentration of carbon dioxide in the acidic environment of the host vesicle. Eventually the food vesicle membrane of the host became the single membrane of chloroplast endoplasmic reticulum surrounding the chloroplast. It is probable that the plastid of the euglenoids evolved by the capture of a green-algal chloroplast. The plastids of the dinoflagellates and apicomplexans probably are derived from an endosymbiotic red-algal chloroplast.

It appears that algae with chloroplast endoplasmic reticulum were selected for in evolution because of their ability to outcompete other algae in environments which are low in dissolved CO2. Before explaining the mechanism by which these algae are able to outcompete, it is necessary to understand the equilibria governing the distribution of carbon species in water.

DINOPHYCEAE

These organisms are important members of the plankton in both fresh and marine waters, although a much greater variety of forms is found in marine members. Generally the Dinophyceae are less important in the colder polar waters than in warmer waters. The highly elaborate Dinophysales (Fig. 7.56(d), (e)) are essentially a tropical group.

A typical motile dinoflagellate (Figs. 7.1, 7.2) consists of an epicone and hypocone divided by the transverse girdle or cingulum. The epicone and hypocone are normally divided into a number of thecal plates, the exact number and arrangement of which are characteristic of the particular genus (Figs. 7.1, 7.3, 7.21(b), 7.25(b)). There is a longitudinal sulcus running perpendicular to the girdle. The longitudinal and transverse flagella emerge through the thecal plates in the area where the girdle and sulcus meet. The longitudinal flagellum projects out from the cell, whereas the transverse flagellum is wave-like and is closely appressed to the girdle. The cells can be photosynthetic or colorless and heterotrophic. Photosynthetic organisms have chloroplasts surrounded by one membrane of chloroplast E.R., which is not continuous with the outer membrane of the nuclear envelope. Chlorophylls a and c2 are present in the chloroplasts, with peridinin and neoperidinin being the main carotenoids. About half of the Dinophyceae that have been examined by electron microscopy have pyrenoids in the chloroplasts (Dodge and Crawford, 1970). The storage product is starch, similar to the starch of higher plants (Vogel and Meeuse, 1968), which is found in the cytoplasm.

DICTYOCHOPHYCEAE

These golden-brown algae are characterized by tentacles or rhizopodia on basically amoeboid vegetative cells (Moestrup, 1995; Preisig, 1995). Amoeboid cells are relatively rare among the algae, being mostly restricted to the Dictyochophyceae and the Xanthophyceae (Hibberd and Chretiennot-Dinet, 1979). The algae in the Dictyochophyceae have been previously classified in the Chrysophyceae, although molecular evidence shows them to be most closely related to the Pelagophyceae (Cavalier-Smith et al., 1995) or Eustigmatophyceae (Daugbjerg and Andersen, 1997).

Classification

The Dictyochophyceae can be divided into three orders (Preisig, 1995):

1. Order 1 Rhizochromulinales: marine and freshwater unicells with tentacles.

2. Order 2 Pedinellales: unicells with a long anterior flagellum and a second flagellum reduced to a basal body, usually three to six chloroplasts (if chloroplasts are present), marine and freshwater.

3. Order 3 Dictyocales: marine unicells with an external silicified skeleton.

Rhizochromulinales

This order contains the more primitive organisms in the order (O'Kelly and Wujek, 1995). Rhizochromulina (Fig. 14.1(a), (b)) has amoeboid non-flagellated vegetative cells with many fine beaded-filipodia and a single golden-brown chloroplast (Hibberd and Chretiennot-Dinet, 1979). The fusiform zoospore has a single tinsel flagellum with a second basal body in the protoplasm (Fig. 14.1(b)). Chrysoamoeba (Fig. 14.1(d)) lives as a solitary amoeba for the greater part of its life cycle, transforming into swimming cells with a single long flagellum only for short periods. In Phaeaster (Fig. 14.1(c)), the anterior portion of the cell is drawn out into rhizopodia.

RAPHIDOPHYCEAE

The Raphidophyceae, or chloromonads, have chlorophylls a and c, and two membranes of chloroplast endoplasmic reticulum. The anterior flagellum is commonly tinsel, whereas the posterior flagellum is naked (Figs. 18.1, 18.2, 18.3). The freshwater species of the Raphidophyceae are green, whereas the marine forms are yellowish and contain the carotenoid fucoxanthin (Vesk and Moestrup, 1987). The closest relatives of the Raphidophyceae are the Eustigmatophyceae and the Chrysophyceae (Cavalier-Smith and Chao, 1996).

Marine species are euryhaline and eurythermic (tolerant of a wide salinity and temperature range) and occur in temperate and subtropical waters worldwide. Marine genera are Chattonella (Fig. 18.3), Fibrocapsa (Fig. 18.1(b)), and Heterosigma (Fig. 18.1(a)). Many of the marine species produce neurotoxic compounds that are similar to brevetoxin (Fig.18.2).

Uptake of the toxin by fish results in depolarization of nerves supplying the heart. This reduces the heart rate, thereby lowering blood pressure, which in turn affects the transfer of oxygen to the gill lamellae, creating hypoxic conditions that lead to fish mortality (Tyrrell et al., 2001).

Toxic red-tide blooms of the marine Chattonella antiqua and Heterosigma carterae (Taylor, 1992) have occurred in the Seto Inland Sea in Japan (Watanabe et al., 1988). These red tides occurred in the summer when a salinity and temperature stratification occurred at a depth of 5−10 meters. There was little mixing of waters above and below the stratified layer resulting in the upper layer being deficient in nutrients while the bottom layer was anaerobic.

Algae with two membranes of chloroplast endoplasmic reticulum (chloroplast E.R.) have the inner membrane of chloroplast E.R. surrounding the chloroplast envelope. The outer membrane of chloroplast E.R. is continuous with the outer membrane of the nuclear envelope and has ribosomes on the outer surface (Fig. V.1).

The algae with two membranes of chloroplast E.R. evolved by a secondary endosymbiosis (Fig. V.1) (Lee, 1977) when a phagocytic protozoan took up a eukaryotic photosynthetic alga into a food vesicle. Instead of being phagocytosed by the protozoan, the photosynthetic alga became established as an endosymbiont within the food vesicle of the protozoan. The endosymbiotic photosynthetic alga benefited from the acidic environment in the food vesicle that kept much of the inorganic carbon in the form of carbon dioxide, the form needed by ribulose bisphosphate/carboxylase for carbon fixation (see Part IV for further explanation). The host benefited by receiving some of the photosynthate from the endosymbiotic alga. The food vesicle membrane eventually fused with the endoplasmic reticulum of the host protozoan, resulting in ribosomes on the outer surface of this membrane, which became the outer membrane of the chloroplast E.R. Through evolution, ATP production and other functions of the endosymbiont's mitochondrion were taken over by the mitochondria of the protozoan host, and the mitochondria of the endosymbiont were lost. The host nucleus also took over some of the genetic control of the endosymbiont, with a reduction in the size and function of the nucleus of the endosymbiont.

Algae are organisms that have plastids, or organisms that are derived from cells whose ancestors possessed plastids. Until 1994, it was thought that the apicomplexa did not have plastids (and consequently were not covered in phycology textbooks). Then it was shown that a known organelle in many apicomplexa was actually a reduced colorless plastid called an apicoplast (Fig. 8.1) (Wilson, 1993; Wilson et al., 1994). Molecular studies have shown that the apicoplast and dinoflagellate plastids originated from red algae by a single endosymbiotic event that occurred relatively early in eukaryotic evolution (Fast et al., 2001).

The discovery of the apicoplast generated considerable interest since most apicomplexans are unicellular endoparasites that cause some of the most significant tropical diseases (Foth and McFadden, 2003). Malaria in humans is produced by the apicomplexan Plasmodium. About 300 million people are infected with malaria, leading to one million deaths annually (Ralph et al., 2004). Apicomplexans cause other serious diseases in livestock and humans, such as cryptosporidiosis, babesiosis (Texas cattle fever), theileriosis (East Coast fever), and toxoplasmosis. The realization that these endoparasites were once algae raised hopes that the apicoplast might be a drug target for two reasons. The first is that the apicoplast is essential for the survival of Plasmodium and Toxoplasma. The second is that drugs effective against prokaryotic organisms might be effective against the apicoplast since all plastids originally evolved from endosymbiotic prokaryotic cyanobacteria.